AB SLC503 PLC Problems

[automa 0]

Hi everyone, I have to load a program in a SLC503 PLC on a old piece of equipment that we purchased. I have no experience with Allen Bradley equipment, and google searches have not yielded any results. The PLC was cycling on and off and during a check of the input power I found it to be 28-29 Volts. I installed a DC-DC power conditioner and now have to much current draw >2amps. Any idea what would cause this? I assume the 24VDC supplied to the CPU is only for the power of the processor and back plane operations. Could something be wrong with one of these?

[Ken Roach 194]

Is the controller still cycling on and off ? That's indicative of an undersize power source or a damaged 1747 power supply. The 1747-P3 range is 19.2 to 28.8 V DC, and the bigger 1747-P7 power supply is designed to work with 10 to 30 volts DC, but I agree that a nominal 24V is best. You can use the SLC Modular Hardware User Guide to calculate the backplane load at both 24V and 5V DC, and that might help you estimate how much load the controller will place on the bulk power supply. If I was troubleshooting this, I would disconnect all the I/O wiring and power up just the SLC and its I/O modules. I've seen lots of systems that exhibited "cycling' behavior because they powered up and immediately turned on a faulty or overloaded device, which then causes the input power to dip and repeats the cycle. Often there is smoke !

[PLCMentor.com 60]

Wow I have too many questions. There are many factors that could be at work here. Two amps doesnt seem like a huge amount of current draw at 24VDC, but I guess it could be on some systems. First what size is the SLC power supply (ie, what is the amp rating)? What size rack and what I/O cards? Is the SLC power supply used to power any cards that require external power? All of these things will affect your current draw. That all said, my gut feeling from what you said the system was doing is that you have a bad SLC power supply.

[PLCMentor.com 60]

Well of course it goes without saying that everything runs better when you get all the smoke out of the system...